Maintaining a properly focused image is critically important in film and television productions. This task is complicated by the fact that many shots require a moving object to be kept in focus or require different objects at different distances from the camera to be in focus at different times during the shot. Before a shot, the person responsible for focusing the camera typically prepares for the shot by carefully measuring the distance to each object that is to be in focus during the shot. These distances are then recorded for use during the shot, such as by marking the focusing ring on the camera lens with the measured distances. During the shot, a “focus puller” adjusts the focusing ring to bring each object into precise focus at the desired time. This method obviously relies on the skill of the focus puller. It is difficult enough to maintain proper focus with stationary objects. If the camera or the subjects to be photographed are moving, it becomes even more difficult to maintain the proper focus. Furthermore, this method is time consuming since careful measurements must be taken and recorded before each shot. While this is being done, the cast and the rest of the production crew must often remain idle.
U.S. Pat. No. 8,121,471 discloses a method and apparatus for automating the camera focusing process. In a particular embodiment described therein, left and right video cameras flank the principal photographic camera. The video cameras are coupled to respective video monitors, each of which has a vertical cursor line superimposed in the middle of the screen representing 90°. A cursor controller allows this line to be moved left and right. As the line is moved left or right to track a desired point of focus on the camera subject, the value increases or decreases from 90°. Software interprets the cursor displacement and determines a real world angular value based on calibration of the focusing system. The angular values are then used to compute the focal distance between the principal camera and the subject.
While the method and apparatus of U.S. Pat. No. 8,121,471 are significant improvements over the prior art, further improvements have been developed.